(1) Field of the Invention
The present invention relates to an electronic weighing apparatus, and more particularly to an electronic weighing apparatus which detects weight of a subject by variation in capacitance, converts an oscillation output of an oscillating circuit corresponding to the above variation in capacitance into weight and displays the converted value on a display.
(2) Description of the Prior Art
Conventional electronic weighing apparatuses of the above type are disclosed in Japanese Utility Model Publication No. 62-111630 and GB No. 2047410 (Japanese Patent Publication No. 55-147317). The electronic weighing apparatus disclosed in the former employs a solar battery as a power source.
In this type of electronic weighing apparatus, however, enough circuit current cannot be obtained by a solar battery only. That is, although a circuit current of about 150 .mu.A is required to operate the apparatus, the electronic weighing apparatus is usually used in a place such as a kitchen where an incandescent lamp or a fluorescent lamp is used as a light source and where electric current obtained from the solar battery is 10 .mu.A at most. Therefore, it is necessary to use the solar battery with another battery acting as a supplementary battery.
In this case, if the solar battery and the supplementary battery are only connected in parallel, the supplementary battery continues to supply electric current even in a dark place. The weighing apparatus has a characteristic that it is hardly used in such a place because it has a purpose of weighing a subject and displaying the measured value. Therefore, the electric current supplied from the supplementary battery is wasted. A conventional power source employing a solar battery with another battery entails the above problem.